Conventionally, lithography is often used to manufacture an integrated circuit device. In lithography, a resist film is formed on a patterning material; an optical image of a circuit pattern is formed on the resist film by irradiating light onto the resist film via a mask in which the circuit pattern is formed; and the resist film is selectively exposed. Then, by developing the resist film after the exposure, the exposed portions of the resist film or the portions of the resist film not exposed are removed; and the resist pattern is formed. Thus, the circuit pattern of the mask is transferred onto the resist pattern. Then, the patterning material is patterned using the resist pattern as a mask.
However, because the optical image formed on the resist film and the resist pattern after the development do not always match due to various factors, it is necessary to design the circuit pattern of the mask to appropriately form the resist pattern. Therefore, in the design of the mask, a simulation is used to evaluate the resist pattern that will be formed using some circuit pattern of the mask.